Transcript Title Page - Vibration Equipment – Vibration Analysis

Vibration Basics
and Shaker Selection
7/16/2015
1
Determining Shaker Sizing
Proper Shaker selection requires application of
Newton’s Second Law of Motion:
Force = Mass x Acceleration (F=MA)
Vibration systems have output forces ratings defined
in terms of:
Sine force: lbs (kN) peak
Random force: lbs (kN) rms
Shock force: lbs (kN) peak
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2
Applying Newton’s Law
In Shaker Selection
Suitability of a Specific Test System can be evaluated in
terms of the following:
Force Requirement (lbf)
UUT + Fixture + Armature x G = F x 1.30= Desired
Force Shaker System
Maximum Displacement
Determined by test environment
Maximum Velocity
Determined by test environment
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3
F=ma
Determining Moving MASS
The mass value (M) in the initial formula of F = MA
must include all moving masses attached to the
shaker armature surface including the armature mass
itself: shaker armature + head expander or slip plate
with its driver bar + test specimen + specimen
interface fixture, including bolts and bearing stiction
if the system is driving a horizontal plate using
hydrostatic bearings.
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Determining and Evaluating
Mass
Test Articles, Slip Tables, Head Expanders and
Fixtures
Size, Mass and Frequency Response
Overturning Moment/Guidance Issues
(UUT+Fixture) x CG x G x Q= lbin
Slide Plate: L x W x PSI (14) x effective area= lbin
Desired Resonance:
Frequency x (L x W)/ 209000=Thickness
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Specimen Specifics
In addition to your test specification, the following
test article data is required to determine the
appropriate system for your test requirements:
Specimen
Specimen
Specimen
Specimen
Specimen
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Description
Test Mass
Dimensions
Center of Gravity (CG)
Mounting Considerations
6
Fixture Specifics
Test fixtures effect mass and resonance and must be
considered carefully. The following concerns should be
addressed in selecting a shaker system:
Do your fixtures exist or will they require design and
fabrication?
What are or will be the approximate dimensions
(estimate if necessary) of the fixturing?
What is or will be the approximate mass (estimate if
necessary) of the fixturing?
Are there any mounting issues (bolt pattern, size)?
Will a head expander be required?
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F=ma
Test Specifications
The maximum Acceleration for the F = MA estimate is
derived from the test specification:



for Sine vibration (G-peak)
for Random vibration (G-rms)
for Classical Shock pulses (G-peak)
The operator must be cognizant of the maximum
displacement and velocity of any given test parameter to
insure they don’t exceed the systems capabilities
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Evaluating the Test Specifications
Waveform:





Sine
Random
Classical Waveform Shock
SRS Shock
Mixed Mode (Sine on Random and Random on Random)
Time Replication
Test Magnitude
Test Frequency Range
Test Duration
Three Axis Testing Required ?
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9
Understanding Random
Vibration
Random vibration stated force ratings are
determined with guidance of ISO 5344. ISO 5344
specifies use of a flat 20 Hz to 2000 Hz spectrum
with a test load of three to four times the armature
mass. This is done to achieve continuity of ratings
between different manufacturers. By use of the nonresonant three to four time armature mass load the
resonant frequency of the shaker armature under
test typically will fall below 2000 Hz. This enables
the system to gain free energy at the higher
frequencies.
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Real World Random Vibration
Typical “real life” Random tests don’t always have
test loads of three to four times the armature weight
and test input profiles are gaussian in nature rather
than flat. Narrow band Random profiles that don’t
excite the armature resonance and have test fixtures
that are highly damped may require system de-rating
of up to 30%.
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11
Effects of Resonance
Every mechanical structure has a resonant
frequency, which may result in a significant dynamic
force absorber at certain frequencies. This phenomena
must be taken into account during the estimating
process. The force rating defined by the manufacture is
rated at the armature surface. If the test system has
associated fixtures, head expanders, slip tables, etc.
that act as force absorbers and have been defined as a
control accelerometer locations, then the shaker may
be over driven. It is always advisable to have
monitor accelerometer attached to the armature
surface to determine the “true force” that is being
achieved.
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12
F=ma
Calculating Required Force
Double Click on our Microsoft Excel® Shaker Selection
Calculator (next slide) for determining the minimum system
force rating requirements needed for your application
Fill in all applicable RED field values
It is always recommended that you verify your calculations with
a sales engineer prior to purchasing a system
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13
Shaker Selection Worksheet
F = MA
Note: Input applicable values in fields shaded RED
Mass (M)
Acceleration (A)
Vertical Testing:
Test Levels:
Test Specimen Mass:
Specimen Interface Fixture Mass:
Armature Mass:
Head Expander Mass:
Associated Mounting Hardware (Estimate):
Total Moving Mass:
0.0
0.0
0.0
0.0
0.0
Random (Grms):
Sine (Gpk):
Classical Shock (Gpk):
0.0
0.0
0.0
0.0
Horizontal Testing:
Test Specimen Mass:
Specimen Interface Fixture Mass:
Armature Mass:
Drive Bar Mass:
Horizontal Slip Table Mass:
Bearing Line Table Effective Moving Mass:
Associated Mounting Hardware (Estimate):
Total Moving Mass:
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Minimum lbf. Rating Required (F):
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0 lbf. Sine
0 lbf. Random
0 lbf. Shock
0
0
0
0
0
0
14